Increased body temperature is a perfectly natural, and perfectly safe part of exercise. Likewise, slight fever is a perfectly natural, and perfectly safe part of getting a cold.
Although these two phenomena are totally safe individually, they are NOT safe when blended together. Exercising with a fever can be incredibly dangerous!
Your body needs to stay between 36.5 - 37.5 degrees in order to function optimally. If your core body temperature increases within this range you might feel uncomfortable, but your muscles, skin, organs etc. will still be functioning perfectly well.
If your body temperature increases to around 37.5 - 38 degrees after exercise or as a result of a virus, your muscles will begin to feel stiff and sore, you might develop some temporary skin rashes, and you might notice changes to your bowel activity. You'll definitely feel uncomfortable, but you're still safe.
If you start exercising WITH a virus, the temperature can increase further. If your body temperature breaks over 38 degrees, things begin to get more serious. Your muscles will become more stiff/sore while simultaneously getting quite week; your skin will become itchy and break out in more rashes; you breathing will become very rapid, your bowel will just stop, and your brain begins to be effected. Your behaviour can change, and you might even have a seizure.
Luckily, very high body temperatures don't happen often in the general population (elderly and the very thin excepted). For most people, it takes either a very strong virus, or exercising with a virus to push us over 38 degrees.
Considering the risks of hyperthermia, the solution is very simple. Don't exercise while you're sick. Take a week off, and return to the gym without muscle/skin/organ/brain damage.
If you want more information on hyperthermia, email me directly via the contact page. If you want specific information about your own injury or if you're after treatment for an injury, contact one of my clinics directly to make an appointment. Details of those clinics can be found here.
Dr Mitch Clark